Streptozotocin toxicity in vitro depends on maturity of neurons

Neurogenesis impairment with glial activation in the hippocampus-connected regions of intracerebroventricular streptozotocin-injected mice

Adult neurogenesis in the hippocampus and subventricular zone (SVZ) is impaired by intracerebroventricular administration of streptozotocin (icv-STZ) to rodents. Although neural cells in the several brain regions which connect with the hippocampus or SVZ is thought to be involved in the adult neurogenesis, few studies have investigated morphological alterations of glial cells in these areas. The present study revealed that icv-STZ induces reduction of neural progenitor cells and a dramatic increase in reactive astrocytes and microglia especially in the hippocampus and various hippocampus-connected brain areas. In contrast, there was no significant neuronal damage excluding demyelination of the stria medullaris. The results indicate the hippocampal neurogenesis impairment of this model might be occurred by activated glial cells in the hippocampus, or hippocampus-connected regions.

A systematic review for the development of Alzheimer's disease in in vitro models: a focus on different inducing agents

Alzheimer's disease (AD) is the most common progressive neurodegenerative disease and is associated with dementia. Presently, various chemical and environmental agents are used to induce in-vitro models of Alzheimer disease to investigate the efficacy of different therapeutic drugs. We screened literature from databases such as PubMed, ScienceDirect, and Google scholar, emphasizing the diverse targeting mechanisms of neuro degeneration explored in in-vitro models. The results revealed studies in which different types of chemicals and environmental agents were used for in-vitro development of Alzheimer-targeting mechanisms of neurodegeneration. Studies using chemically induced in-vitro AD models included in this systematic review will contribute to a deeper understanding of AD. However, none of these models can reproduce all the characteristics of disease progression seen in the majority of Alzheimer's disease subtypes. Additional modifications would be required to replicate the complex conditions of human AD in an exact manner. In-vitro models of Alzheimer's disease developed using chemicals and environmental agents are instrumental in providing insights into the disease's pathophysiology; therefore, chemical-induced in-vitro AD models will continue to play vital role in future AD research. This systematic screening revealed the pivotal role of chemical-induced in-vitro AD models in advancing our understanding of AD pathophysiology and is therefore important to understand the potential of these chemicals in AD pathogenesis.

A review of the biological effects of Myrtus communis

The World Health Organization stated that 1.6 million deaths worldwide were caused by contact with chemicals and toxins in 2019. In the same year, the Centers for Disease Control and Prevention stated that natural toxins caused 3960 deaths. Myrtus communis, also known as common Myrtle, is a flowering plant native to the Mediterranean region. Myrtle has been traditionally used to treat diarrhea, inflammation, bleeding, headache, pulmonary and skin diseases. This review was performed to assess Myrtle's protective and therapeutic efficacy against various chemical, natural, and radiational noxious. Multiple databases such as PubMed, Web of Sciences, and Scopus were investigated without publication time limitation. Recent studies have demonstrated its potential as a protective agent against both natural and chemical toxins. One of Myrtle's most significant protective properties is its high antioxidant content. Studies have shown that the antioxidant properties of Myrtle can protect against harmful substances such as heavy metals, pesticides, and other environmental toxins. Additionally, Myrtle has anti-inflammatory properties that can help reduce the damage caused by long-term exposure to toxins. The anti-inflammatory and antimicrobial properties of Myrtle have also proven effective in alleviating gastrointestinal conditions such as gastric ulcers.

Alterations in tanycytes and related cell populations of arcuate nucleus in streptozotocin-induced Alzheimer disease model

It is assumed that dysfunction of tanycytes could be one of the components of pathogenesis of both Alzheimer disease and type 2 diabetes mellitus. The study was aimed to assess alterations in the tanycyte morphology in the Alzheimer disease model. The 3 mg/kg streptozotocin dose was injected in the lateral ventricles of Wistar rats in order to model the Alzheimer disease. Alterations in hypothalamic tanycytes were assessed 2 weeks, 4 weeks, 3 months and 6 months after administration of the toxin. Immunohistochemistry was used to identify the protein markers of tanycytes (vimentin, nestin), astrocytes (GFAP, glutamine synthetase) and neurons (HuC/D), as well as to assess cell proliferation (with the use of Ki67 protein) and mitochondrial alterations (mitochondrial complex IV, PGC1a). Administration of streptozotocin lead to β-amyloid accumulation in hypothalamus and ventricular enlargement (p < 0.001). Streptozotocin damaged both α1/α2 tanycytes and β1 tanycytes. The intensity of vimentin staining in α1/α2 tanycytes decreased by week 4 (p = 0.003), and in β1 tanycytes it decreased in three months (p < 0.001). The same trend was observed for nestin. The number of Ki67+ nuclei decreased (p < 0.05), and the expression of proteins associated with mitochondria changed. The density of hypothalamic tanycytes decreased by week 4 after administration of the toxin. Moreover, astrocyte activation was revealed. However, no prominent damage to both astrocytes and neurons was observed within four weeks after administration of streptozotocin. The revealed high tanycyte vulnerability to streptozotocin is in line with the hypothesis of the role of damage to hypothalamic structures in both local and systemic metabolic disorders occurring in the Alzheimer disease models.

Toxic Effect of Streptozotocin on Cultured Mouse Hippocampal Neurons

In primary dissociated hippocampal cell cultures from 18-day-old mouse embryos, streptozotocin in concentrations of 2-5 mM produced a dose-dependent cytotoxic effect on day 3 in vitro, whereas on day 11 of culturing, the neurons were resistant to streptozotocin. The neurons in the 3-day cultures were functionally immature, which was seen from their weak spontaneous bioelectric activity in the form of rare single action potentials; by day 11 of culturing, the neurons reached a high level of differentiation and their functional properties acquired a character of network burst activity. Thus, streptozotocin had the most pronounced cytotoxic effect on immature hippocampal neurons in vitro.

Prevention of streptozotocin‑induced Neuro‑2a cell death by C8‑B4 microglia transformed with repetitive low‑dose lipopolysaccharide

Diabetes‑associated neuronal dysfunction (DAND) is one of the serious complications of diabetes, but there is currently no remedy for it. Streptozotocin [2‑deoxy‑2‑(3‑methy1‑3‑nitrosoureido) D‑glucopyranose; STZ] is one of the most well‑established diabetes inducers and has been used in vivo and in vitro DAND models. The aim of the present study was to demonstrate that C8‑B4 microglia transformed by the stimulus of repetitive low‑dose lipopolysaccharide (LPSx3‑microglia) prevent STZ‑induced Neuro‑2a neuronal cell death in vitro. The ELISA results showed that neurotrophin‑4/5 (NT‑4/5) secretion was promoted in LPSx3‑microglia and the cell viability assay with trypan blue staining revealed that the culture supernatant of LPSx3‑microglia prevented STZ‑induced neuronal cell death. In addition, reverse transcription‑quantitative PCR showed that neurons treated with the culture supernatant of LPSx3‑microglia promoted the gene expression of B‑cell lymphoma‑extra large and glucose‑dependent insulinotropic polypeptide receptor. Furthermore, the inhibition of tyrosine kinase receptor B, a receptor of NT‑4/5, suppressed the neuroprotective effect of LPSx3‑microglia. Taken together, the present study demonstrated that LPSx3‑microglia prevent STZ‑induced neuronal death and that NT‑4/5 may be involved in the neuroprotective mechanism of LPSx3‑microglia.

The Impact of Differentiation on Cytotoxicity and Insulin Sensitivity in Streptozotocin Treated SH-SY5Y Cells

Recently neuronal insulin resistance was suggested playing a role in Alzheimer’s disease. Streptozotocin (STZ) is commonly used to induce impairment in insulin metabolism. In our previous work on undifferentiated SH-SY5Y cells the compound exerted cytotoxicity without altering insulin sensitivity. Nevertheless, differentiation of the cells to a more mature neuron-like phenotype may considerably affect the significance of insulin signaling and its sensitivity to STZ. We aimed at studying the influence of STZ treatment on insulin signaling in SH-SY5Y cells differentiated by retinoic acid (RA). Cytotoxicity of STZ or low serum (LS) condition and protective effect of insulin were compared in RA differentiated SH-SY5Y cells. The effect of insulin and an incretin analogue, exendin-4 on insulin signaling was also examined by assessing glycogen synthase kinase-3 (GSK-3) phosphorylation. STZ was found less cytotoxic in the differentiated cells compared to our previous results in undifferentiated SH-SY5Y cells. The cytoprotective concentration of insulin was similar in the STZ and LS groups. However, the right-shifted concentration–response curve of insulin induced GSK-3 phosphorylation in STZ-treated differentiated cells is suggestive of the development of insulin resistance that was further confirmed by the insulin potentiating effect of exendin-4. Differentiation reduced the sensitivity of SH-SY5Y cells for the non-specific cytotoxicity of STZ and enhanced the relative significance of development of insulin resistance. The differentiated cells thus serve as a better model for studying the role of insulin signaling in neuronal survival. However, direct cytotoxicity of STZ also contributes to the cell death.

Shared cerebral metabolic pathology in non-transgenic animal models of Alzheimer's and Parkinson's disease

Parkinson's disease (PD) and Alzheimer's disease (AD) are the most common chronic neurodegenerative disorders, characterized by motoric dysfunction or cognitive decline in the early stage, respectively, but often by both symptoms in the advanced stage. Among underlying molecular pathologies that PD and AD patients have in common, more attention is recently paid to the central metabolic dysfunction presented as insulin resistant brain state (IRBS) and altered cerebral glucose metabolism, both also explored in animal models of these diseases. This review aims to compare IRBS and alterations in cerebral glucose metabolism in representative non-transgenic animal PD and AD models. The comparison is based on the selectivity of the neurotoxins which cause experimental PD and AD, towards the cellular membrane and intracellular molecular targets as well as towards the selective neurons/non-neuronal cells, and the particular brain regions. Mitochondrial damage and co-expression of insulin receptors, glucose transporter-2 and dopamine transporter on the membrane of particular neurons as well as astrocytes seem to be the key points which are further discussed in a context of alterations in insulin signalling in the brain and its interaction with dopaminergic transmission, particularly regarding the time frame of the experimental AD/PD pathology appearance and the correlation with cognitive and motor symptoms. Such a perspective provides evidence on IRBS being a common underlying metabolic pathology and a contributor to neurodegenerative processes in representative non-transgenic animal PD and AD models, instead of being a direct cause of a particular neurodegenerative disorder.

Lack of insulin resistance in response to streptozotocin treatment in neuronal SH-SY5Y cell line

Recently, it is suggested that brain insulin resistance may contribute to the development of Alzheimer’s disease; therefore, there is a high interest in its investigation. Streptozotocin (STZ) is often used to induce dysregulation of glucose and insulin metabolism in animal and cell culture models. Alteration in insulin sensitivity however, has not yet been assessed in neuronal cells after STZ treatment. We aimed at studying the concentration dependence of the protective effect of insulin on STZ-induced damage using SH-SY5Y cell line. Cells were treated with STZ and cell viability was assessed by resazurin reduction and lactate dehydrogenase release assays. Low serum (LS) medium was used as control damage. The effect of various concentrations (30, 100, 300, 1000 nM) of insulin was studied on cell viability and glycogen synthase kinase-3 (GSK-3) phosphorylation, an indicator of insulin signaling. STZ induced dose- and time-dependent cytotoxicity, its 1 mM concentration exerted a low, gradually developing damage. The cytoprotective effect of insulin was demonstrated in both STZ and LS groups. Its maximal effect was lower in the STZ-treated cells; however, its effective concentration remained largely unaltered. Insulin-induced GSK-3 phosphorylation was similar in the STZ- and LS-treated cells suggesting unchanged insulin signaling. Our present results indicate that STZ does not induce significant impairment in insulin sensitivity in SH-SY5Y cells, thus in this cell line it is not a good tool for studying the role of insulin resistance in neurodegeneration and to examine protective agents acting by improving insulin signaling.

Neurodegenerative Changes in Rat Brain in Streptozotocin Model of Alzheimer's Disease

One of the most common models of sporadic form of Alzheimer's disease is injection of streptozotocin into the lateral ventricles of rat brain. In 3 months after this injection, an increase in the expression of astroglia in the corpus callosum and a decrease in the thickness of the corpus callosum and intensity of its staining with luxol fast blue were observed. This can reflect a decrease in the content of myelinated fibers. In layer V of the sensorimotor cortex, intensive degeneration of neurons was revealed. The lateral ventricles were significantly enlarged and the expression of PSA-NCAM protein, a marker of immature neurons, was reduced in subventricular zone, which can be associated with disturbed neurogenesi.